1. Field of the Invention
The present invention relates to an image display method and system for a plasma display panel. More particularly, the present invention relates to an image display method and system for a plasma display panel that reduces flicker, contour noise, interference patterns, and other such problems when an image is realized by the input of 50 Hz Phase Alternating by Line image signals.
2. Description of the Related Art
A plasma display panel (PDP) is a display device in which a plurality of discharge cells are arranged in a matrix, and the discharge cells are selectively illuminated to restore image data, which are input as electrical signals.
In such a PDP, the display of gray must be possible in order to exhibit the capabilities of a color display device. A gray realization method is used to achieve this, in which a single field is divided into a plurality of sub-fields and the sub-fields are controlled by a process of time sharing.
A major concern for the designer of such display devices is that of flicker. Flicker is closely related to how the human eye perceives images. Generally, flicker becomes more perceptible as screen size is made larger and as display frequency is lowered. In the case where images are realized in a PDP using Phase Alternating by Line (PAL) image signals, both these factors are present such that a significant amount of flicker is generated.
Accordingly, if the PDP is driven at a vertical frequency of 50 Hz using a minimum increase arrangement or using a minimum decrease arrangement, which are sub-field arrangements typically used in PDPs, a great amount of flicker is generated.
Among the factors that make flicker more problematic, since it is not possible to change the screen size, flicker must be reduced by varying frequency. Korean Laid-open Patent No. 2000-16955 discloses a method of reducing flicker by adjusting frequency. In that disclosure, to reduce flicker in a PDP having a large screen and being operated by the input of 50 Hz image signals, sub-fields within a single field are divided into two groups (G1 and G2), and a weight arrangement of the sub-fields in each group is identical or all sub-field arrangements except an LSB (Least Significant Bit) sub-field have the same structure. Further, a feature of that disclosure is that a brightness weighting value in the two sub-field groups is identically distributed. The reduction of flicker with the use of this method is greatly improved over the conventional sub-field arrangement of a minimum increase arrangement or a minimum decrease arrangement.
FIG. 12 is a schematic view of a conventional sub-field arrangement, and FIG. 13 is a schematic view showing an example of On/Off control of each sub-field in grays generating flicker in the case where a conventional sub-field arrangement is used to realize grays. As shown in the drawings, in order to realize the display of 109 grays, 53 grays are displayed in group G1 and 56 grays are displayed in group G2.
Sub-fields SF1 to SF5 are On in group G1; and sub-fields SF3, SF4, and SF6 are On in group G2. Accordingly, in the case of the upper sub-field SF6, the number of lines On in group G1 is 0 since all lines are Off, and the number of lines On in group G2 is 4 since all lines are On such that a weight difference (i.e., the difference in the number of lines On) is 4. Because of this large difference, an illuminating central axis position of each group (G1 and G2) is different, resulting in the generation of flicker. Although only four lines were described in this example, in the case where more lines have the same gray, for example, in the case where all 480 lines in a 480×640 size screen have the same gray, the difference in the number of lines On becomes 480 such that the user sees a considerable amount of flicker.
There are many instances when grays of adjacent pixels in an image displayed on a screen are identical. Accordingly, if an image having identical grays over a number of lines is displayed, flicker that is visible to the human eye is generated as a result of the sub-field weight difference between the sub-field groups (G1 and G2) as described above.
The display of grays in the prior art by distributing brightness weights in each group (G1 and G2) does not reduce flicker in all grays of image signals. That is, when displaying grays, if an uppermost weight of the sub-fields displaying grays assigned to group G1 and an uppermost weight of the sub-fields displaying grays assigned to group G2 are different, a discrepancy in the illuminating central axis positions occurs in the two groups. Flicker is generated as a result.